Because such pumps are generally miniaturized and portable, in order that the patient may circulate freely without being confined to bed and without being under permanent medical supervision, it is indispensable that such pumps be very reliable and provided with security arrangements.
The principle of such pumps is as follows. It consists in using a tube of deformable plastic material which is locally crushed against a fixed casing by means of a rotor driven in rotation by a motor and equipped with presser rollers. The successive pressures exerted by the rollers onto the tube enable drawing in liquid contained in a reservoir and rejecting it through the tube towards the output of the pump. Thus one displaces through the tube a pocket of liquid included between two successive rollers.
It will be readily understood that the distance between each presser roller and the casing against which the tube is crushed must be precisely adapted so as to crush the tube correctly. Effectively, if the presser roller is too close to the casing, it will crush the tube too heavily so that it runs the risk of being deformed and elongated. Inversely, if the tube is not correctly crushed, the pump will not provide the proper quantity of medication.
Consequently, the pump is not reliable which can be dangerous for the patient.
Such problems may arise particularly in pumps of the prior art formed in two modules, such latter being unitable at the moment of utilization thereof. Effectively, in the medical domain, it is frequently sought to provide a pump in two modules, one module containing the elements which must be sterilized and another module containing the elements which cannot resist sterilization. For example one may have one module which contains the rotor and the motor, and one module which contains the reservoir, the tube and the casing. When such two modules are manually assembled, the distance between the rollers of the rotor and the casing is not precise and the problems previously evoked may arise. It is necessary to add to that the dimensional differences of the pump elements due to manufacturing tolerances.
FIGS. 1, 2 and 3 here attached are schematics illustrating the different problems which may arise in this type of prior art pump in two modules.
Such pumps comprise a motor module 1 and a reservoir module 2. The motor module 1 comprises a gripping head 3 and a rotor 4 provided with presser rollers 5. Such module 1 is designed in order to be introduced into the interior of reservoir module 2 in a cavity 6 provided to such effect (arrow SI, introduction sense). The reservoir module 2 comprises a reservoir of liquid 7 coupled by a tube 8 to a needle 9 placed at the output of the pump. The needle 9 is implanted into the circulatory system 10 of the patient. A portion of tube 8 is placed in front of the bottom of cavity 6 which constitutes a support zone 11.
Module 1 is introduced to the interior of the reservoir module 2 in a manner such that on the one hand presser rollers 5 crush tube 8 against the support zone 11 (zone A) and on the other hand the gripping head 3 comes into contact with the periphery of the entry of cavity 6 (zone B), in order to assure impermeability of the pump. Nevertheless, taking into account the manufacturing tolerances of the elements of the different modules, these two conditions are practically never obtained simultaneously. FIGS. 1, 2 and 3 illustrate such contact problems, the distances between such different elements having been exaggerated in order to facilitate explanation thereof.
In the case shown on FIG. 1, the distance between the presser roller 5 and the support zone 11 is too great and tube 8 is not crushed. In this situation the liquid is no longer pumped and remains stationary within tube 8. In an extreme case, the blood of the patient may even risk flowing back to the interior of the pump (arrow F).
In the case shown on FIG. 2, the distance between the presser roller 5 and the support zone 11 is too small and tube 8 is too heavily compressed. Consequently, the liquid no longer circulates within tube 8, the motor driving the rotor 4 is forced to provide a higher couple in order to attempt to overcome such blocking and tube 8 is deformed. Finally, the pump runs the risk of being blocked. Tube 8 may also be too heavily compressed because of a variation of its dimensions due to manufacturing tolerances. Effectively, if tube 8 exhibits over one of its sections a diameter greater than the average diameter for which the distance between the support zone 11 and rollers 5 has been calculated, it will be completely crushed.
FIG. 3 shows a third type of problem. Tube 8 is correctly crushed (zone A), but the contact between the gripping head 3 and the periphery of cavity 6 (zone B) is not perfect. The result thereof is that the pump is no longer impermeable. Thus, when for instance the user washes himself, there is a risk of water penetrating to the interior of the pump and damaging it, in particular in damaging the driving mechanism of the rotor or in bringing about a short-circuit of the battery energizing the motor.
The invention has as its purpose to overcome these difficulties and to increase the flexibility of utilization of peristaltic pumps while assuring a high level of safety.